<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Light ball</title>
    <style type="text/css">
        @keyframes light {
            from {
                box-shadow:0px 0px 4px yellow;
            }
            to {
                box-shadow:0px 0px 16px yellow;
            }
        }
        .light {
            margin:300px;
            width: 100px;
            height: 100px;
            border-radius: 50%;
            animation: light 2s ease-in-out infinite alternate;
        }
    </style>
</head>
<body style="margin:0 auto;">
<div class="light"></div>
</body>
</html>
